bug#18195: 24.3.92; window-screen-lines is not accurate

[martin rudalics]

> He can't: we currently don't expose enough information for Lisp
> programs to perform layout.  E.g., the metrics of glyphs and lines
> that use arbitrary fonts and display images are not easily available
> on the Lisp level, and neither are dimensions and line counts of
> arbitrary regions of the screen (although you could write some clunky
> Lisp to do the latter).  Likewise with dimensions of text in overlays
> and display properties, and with images.
>
> This was never supposed to be needed, and thus was never designed and
> implemented.  If we want to allow such jobs from Lisp, we need to
> close these gaps.

Why would `window-text-pixel-size' fail to provide that?  It might be a
bit clumsy to work with because you have to temporarily show another
buffer in its window but apart from that I see no problems ...

martin